Well we, HTACG - https://www.w3.org/community/htacg/ - who maintain
**Tidy**, are
associated with the W3C - https://www.w3.org/standards/ - which, as you can
read, promotes Web standards, internationally...
But then it is up to the individual browser developers to apply those
standards, and not **all** choose to conform...
As to **why**, can not answer that... but hope this helps with your
question... there is no way to **force** browser developers onto one
path...
You can perhaps help, by only supporting browsers that do conform to the
standards laid down, and write to others, on their respective lists, and
complain...
In general, I am afraid we, as Tidy, can do little about this...